Morgan gets a bath (well, a shower) when he asks for one, or maybe if we decide to have him prettied up for out-of-town guests visiting or something.
Left to his own devices, he'd probably get bathed 3-4 times a year, which is honestly fine. He's never been the type to roll in anything stinky (something that I am eternally grateful for), plus I think if he got bathed much more than that, he would be dry-skin itchy.